Origin of strong intrinsic Kerr effect in FePt and FePd ordered compounds

The magneto-optical spectra of chemically ordered FePt (001) and FePd (001) compounds are studied. The imaginary part of the off diagonal element, oz, of the conductivity tensor has two peaks located in the energy ranges 1.2 - 2 eV (Fe-like transitions) and 4 - 4.5 eV (Pt or Pd like transitions). The strength of these peaks is larger in FePt than in FePd and roughly scales with the spin orbit coupling of Pt and Pd d-bands in the ultraviolet spectral range. Large differences in the Fe dominated low energy side of the spectra suggest a much higher degree of electronic hybridization in FePt than in FePd.